The present invention relates to a means for preventing reverse flow through conductors. More spcifically, the present invention relates to a check valve assembly or device which when situated in a flow conductor, such as a pipe string, will permit the flow of fluids through the conductor only in one direction. In a particular application, a ckeck valve of the assembly of the present invention is adapted to allow well bore fluids, such as drilling fluids, workover fluids, etc., to be injected into the wellbore, but to prevent reverse, upward flow of fluids in the string when equipment failures occur or unexpected high pressure is encountered downhole.
CHECK VALVE DEVICES COMMONLY EMPLOYED IN OIL AND GAS WELLS MAY BE BROADLY PLACED INTO TWO CATEGORIES, THOSE WHICH ARE DESIGNED TO PERMIT A CONTROLLED, UPWARD FLOW OF FLUIDS IN THE WELL TUBING AND THOSE WHICH ARE DESIGNED TO PREVENT ANY UPWARD FLOW OF SUCH FLUIDS.
The first category of check valve are commonly used in production strings and serve to shut down production when necessitated, for example, by equipment failure at the wellhead. These devices commonly employ a flow responsive valve which automatically closes when the upward flow rate of the production fluid exceeds a selected maximum value.
The second category of check valves includes those which are designed to permit only downward flow of fluids into the well tubing, and which automatically close in response to a reverse in the flow direction. Recent improvements in such check valves, illustrated in U.S. Pat. No. 3,850,191, employ a ball element in a recessed side chamber which communicates with the flowstream through a downstream pressure passage. The ball is displaced from the recess by reverse flow to block the tubing.
The many prior art devices, the surface with which the valve element must seat is subjected to the effects of the abrasive and corrosive fluids, such as argillaceous drilling fluids, or acidic workover and fracturing fluids frequently sent down hole from the surface. The erosion and corrosion may cause substantial wear or channeling of the valve seat and any other element in the fluid flow path, such that an imperfect seal is formed when the reverse flow conditions occur.
Another aspect of certain prior art devices is their general reliance on the reverse flow of the fluids, rather than the absence of forward flow, to activate the check valve operation. Under some circumstances, valves of this design may be prevented from closing if the reverse flow occurs too rapidly or forcefully. Moreover, in conventional valve closures, flow of material in the tubing may carry extraneous material into the seat area and block a complete seal.